Ans:In an ecosystem, energy as well as materials travel from one trophic level to the next. Figure 16.2 Trophic (food) level is the level at which an organism feeds in food chain. The first trophic level is made of producers; the second of primary consumers and so on.
Flow of Energy
The flow of energy in different trophic levels of ecosystem is .unidirectional. The following is an overview of the flow of energy in an ecosystem.
Primary source of energy: The Sun is the primary source of energy for all ecosystems. Producers get solar energy and transform it into chemical energy by the process of photosynthesis.
They store this energy in their tissues and also transform it into mechanical and heat energy during their metabolic activities.
The energy in producer's tissues flows to herbivores when producers are eaten. He&ivores transform it into mechanical and heat energy during their metabolic activities, use it for,their body activities and store the rest in their tissues.
Carnivores eat herbivores and get energy. They also use it for "their body activities and store their rest in their tissues. After the death of producers and consumers, theieihergy stored in their tissues is used by decomposers.
Law of Thermodynamics: The storage and expenditure of energy in an ecosystem is in accordance with the basic law of thermodynamics .i.e. 'energy can neither be created nor destroyed but can be transformed from one form into another, In an ecosystem there is:
Constant flow or transfer of energy from the Sun through producers to consumers and decomposers.
A significant decrease in useful.energy during transfer of energy at each trophic level.
Flow of Materials
The materials flow from one trophic level to the next by means of food chains and food webs.
Food chain: A food chain is a series of organisms within an ecosystem, in which each organism feeds on the one before it and is fed by the one after it. For example, following is a food chain in an ecosystem. Figure 16.3
Grass— Grasshopper— Sparrow -Hawk
The base of food chain is always formed by a plant (producer). It is eaten by a primary consumer, which is preyed upon by .a secondary consumer. The secondary consumer may be eaten by a tertiary consumer. A food chain, can therefore, be represented as,
Producer-Primary Consumer-*Secondary Consumer-Tertiary-Consumer .
A food chain involves a nutritive interaction among the biotic components of an ecosystem. Usually there are 4 or 5 trophic levels. Shorter food chains provide greater available energy and vice-versa.Food web: In nature, food chains are very complex, as one organism may be the food source of many other organisms. Thus,instead of a simple linear food chain, there is a web-like structure formed by these interlinked food chains. Such interconnected food chains collectively make 'food web'. Food web can be defined as, "a network of food chains which are interconnected at various trophic levels" Figure 16.4